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British gaming company Improbable has claimed that a change in the terms of service for the popular Unity game engine has effectively blocked the use of its 'SpatialOS' virtual world building technology in upcoming video games.

Improbable, the $2bn rated start-up that received a £390m investment from Softbank, released a statement on its website saying that "due to a change in Unity’s terms of service, all existing SpatialOS games using Unity, including production games and in development games of all developers, are now in breach of Unity’s license terms".

SpatialOS is cloud-based technology that allows developers to help build and service virtual worlds for multiplayer games. The technology needs to be integrated with an existing game engine such as Unity, Cryengine or Fortnite creator Epic's Unreal engine.

Unity is one of the most popular game engines in the world, famed for its accessibility and ease of use. While many larger game developers often favour Unreal or their own proprietary technology for PC and console games, Unity is well-suited to mobile games and smaller projects.

The change in the terms of service says that developer may not distribute the Unity engine by means of cloud servers without prior authorisation.

Bossa Studios' World's Adrift is still online for now

Improbable said that Unity clarified that the change would "specifically disallow services like Improbable’s to function with their engine." Additionally, Improbable said that it has had its license to work with Unity revoked due to breaching the new terms of service in an "unspecified way", which will affect the company's ability to support existing games.

Games that are already live are now in "legal limbo", according to Improbable, as they are also effectively in breach of Unity's terms of service by using SpatialOS.

However, Unity said in its own blog post that Improbable's claims were 'incorrect' and that while the British developer's access to Unity has been revoked, Unity "made it clear that anyone using SpatialOS will not be affected."

Space-faring MMO Lazarus was temporarily taken offline by developer Spilt Milk Studios before later being reinstated. Another game that uses both Unity and SpatialOS, World's Adrift, is still online for now, with developer Bossa Studios tweeting: "whatever is happening in the background outside of our control, our focus is ensuring players are looked after and your memorable experiences in the game are protected."

"Overnight, this is an action by Unity that has immediately done harm to projects across the industry," said Improbable. "Including those of extremely vulnerable or small scale developers and damaged major projects in development over many years."

Improbable said it hoped to find a quick resolution.

"We believe this unfortunate and counterproductive action to be an error in judgement or coordination failure within Unity," said Improbable. "We are urgently working to clarify this situation and believe that a swift resolution may be possible."